This report provides guidance on whether an agency should calibrate the safety performance functions (SPFs) from the Highway Safety Manual (HSM) or develop jurisdiction-specific SPFs. The guidebook discusses the factors to be considered in the decision-making process. It is intended to be of use to practitioners at state and local agencies and to researchers. The guide recommends sample sizes, years of data, staff hours needed for data collection and preparation, and staff hours needed for statistical analysis. The steps that agencies need to take in order to obtain the final SPF to be used in a jurisdiction include:

• Determine intended use of SPF.
• Determine facility type.
• Identify existing SPF.
• Consider sample size necessary for calibrating SPF.
• Consider roadway data necessary for calibrating SPF.
• Calibrate existing SPF.
• Assess quality of calibration factor.
• Consider statistical expertise necessary for developing SPF.
• Consider sample size necessary for developing SPF.
• Determine crash type to be addressed by SPF.
• Develop SPF.